Topological thermal Hall effect of magnetic monopoles in the pyrochlore U(1) spin liquid

Abstract

“Magnetic monopole” is an exotic quantum excitation in three-dimensional U(1) spin liquid, and its emergence is purely of quantum origin and has no classical analog. We predict topological thermal Hall effect (TTHE) of “magnetic monopoles” and present this prediction through non-Kramers doublets on a pyrochlore lattice. We observe that when the external magnetic field polarizes the Ising component of the local moment, internally this corresponds to the induction of emergent dual U(1) gauge flux for the “magnetic monopoles.” The motion of “magnetic monopoles” is then twisted by the induced dual U(1) gauge flux. This emergent Lorentz force on “magnetic monopoles” is the fundamental origin of TTHE. Therefore, TTHE would be a direct evidence of the “monopole” gauge coupling and the emergent U(1) gauge structure in pyrochlore U(1) spin liquid. Our result does not depend strongly on our choice of non-Kramers doublets for our presentation and can be well extended to Kramers doublets. Our prediction can be readily tested among the pyrochlore spin liquid candidate materials. We give a detailed discussion about the expectation for different pyrochlore magnets.